(232e) CO2 Utilization in the Production of Ethylene Oxide

A conventional hydrocarbon feedstock that is of particular interest for CO₂ utilization is ethylene, which is used to make ethylene oxide. Ethylene oxide is an important feedstock for the chemical industry and is used to make many useful products such as polyurethanes, polyols, glycols, nitriles, alcoholamines, and ethers. Ethylene oxide is manufactured by several closely related industrial processes by major chemical makers worldwide (e.g., DOW Chemical, Japan Catalytic Company, Shell International Chemicals, Sumitomo Chemical, BASF, Scientific Design).

The chemical methodology by which ethylene oxide is currently produced is the partial oxidation of ethylene using oxygen (this process is called epoxidation). A silver-based catalyst is used, and either air or preferably oxygen is the oxidant. Ethylene epoxidation is performed at lower temperatures (220 to 280°C) compared with other selective oxidation processes and at high pressure (10 to 30 bar).¹

The Captured CO₂ Catalyst for the Production of Ethylene oxide (C3-PEO), a technology being developed at RTI International, aims at producing ethylene oxide—a high-value chemical—while consuming CO₂—a greenhouse gas. This technology is based on novel catalysts utilizing the following key discoveries:

1. Abstraction of oxygen from CO₂ using the reduced mixed-metal oxide catalysts

2. Transfer of the abstracted oxygen from CO₂ to react with hydrocarbons to form desired products

3. Operation at temperatures which make these catalysts commercially practical to produce ethylene oxide

   Our proposed process uses a cofeed reactor as shown in Figure 1. The proposed ethylene oxide process will have a concentrated CO byproduct stream, which could be used for the manufacture of many products such as methanol, dimethyl ether, acetic acid, acetic anhydride, vinyl acetate, styrene, terephthalic acid, formic acid, n-butanol, 2-methylpropanal, acrylic acids, neopentylacids, propanoic acid, dimethyl formamide, and Fischer-Tropsch hydro­carbons.² Therefore, the two marketable product streams from the proposed process are ethylene oxide and CO, which are both valuable intermediates for the petrochemical industry.

Figure 1. Conceptual schematic of the transport reactor process used in this process.

RTI has improved on its previous catalyst formulations for CO₂ utilization³ and developed families of catalysts which can both remove oxygen from CO₂ and transfer the oxygen to ethylene to make ethylene oxide. The catalyst families are based on metal oxide phases which were found to be similar to iron in terms of reacting with CO₂, but are more selective than iron for ethylene epoxidation. Improvements on the production of ethylene oxide have been made by the use of promoters, probing the catalyst support to identify a correlation with support acidity, and observing the impact of surface area on dispersion. Ethylene oxide has been produced at small scale in the fixed-bed catalyst test reactor in both a continuous cofeed and a transport mode of operation. However, a cofeed system was found to be optimal and studied for scale-up of the technology.

Life cycle analysis has shown that the process avoids more than 2.8 kg of CO₂ per kg of ethylene oxide produced. Techno-economic analysis results show that the process can produce an IRR above 15%, and sensitivity analyses reveal the most important factors regarding the economic viability of the technology. We have compared the RTI CO₂ oxidation process with the state of art partial oxidation process and found that the new process can be economically favorable depending on market conditions.

(1) Chongterdtoonskul, A.; Schwank, J. W.; Chavadej, S. Journal of Molecular Catalysis A: Chemical 2013, 372.

(2) Kolb, K. E.; Kolb, D. Journal of Chemical Education 1983, 60, 57.

(3) Shen, J. P.; Mobley, P. D.; Douglas, L. M.; Peters, J. E.; Lail, M.; Norman, J. S.; Turk, B. RSC Advances 2014, 4, 45198.

Keywords: CO2 Utilization, Ethylene Epoxidation